1. Field of the Invention
The present invention relates to an optical sensor (photo-electric sensor) where the photoelectric effect of photoconductive materials is utilized.
2. Description of the Related Art
FIGS. 3 and 4 schematically illustrate a conventional optical sensor. In the figures, there is shown a substrate 1. A rectangular photoconductive body 2 is formed on this substrate 1. This photo-conductive body 2 is a thin film made of such materials as amorphous silicon hydroxide and cadmium sulfide. A pair of electrodes 3A and 3B which are shaped as a thin-film band, are provided on the photoconductive body 2 so as to derive photoelectric current under the condition that these electrodes 3A and 3B are positioned opposite to each other via a gap 4 having a predetermined interval "L". These electrodes 3A and 3B may be fabricated by employing the known thin-film forming means, e.g., a patterning method for evaporating a metal such as aluminium and for performing etching by way of photo-lithography, and a patterning method for evaporating aluminium via a metal mask.
In such a conventional optical sensor, the photoelectric current flows between the electrodes 3A and 3B in response to the intensities of light incident upon the gap 4. The photoelectric current "I" flowing through these electrodes 3A and 3B is directly proportional to a width "W" of each of the electrodes 3A and 3B, whereas the photoelectric current "I" is inversely proportional to the gap "L" between these electrodes. That is to say,
I.varies.W/L . PA1 t.varies.L.sup.2. PA1 a second notch portion formed in said electrode under the condition that all of the second notch portion other than a portion thereof communicated with said first notch portion is closed. PA1 a pair of &lt;-shaped electrodes each having a width of "W", positioned opposite to each other on said photoconductive body via first and second gaps each having an interval of "L" defined by the opposite electrodes; PA1 a first notch portion having a width of "L" and a length greater than "W/2", positioned at a substantially center of one of said opposite electrodes with being opened to said two gaps; and PA1 a second notch portion formed in said electrode in such a manner that all of the second notch portion other than a portion thereof communicated with said first notch portion is closed.
Moreover, the response speed "t" of the optical sensor is directly proportional to the 2nd power of the gap "L", or the squared gap "L"; namely,
Accordingly, to increase the photoelectric current without fabricating a large-sized optical sensor, the gap "L" is necessarily required to be made narrow in order to increase the response speed of the optical sensor. When the gap "L" between these electrodes 3A and 3B is made narrower, there is a risk that the electrodes 3A and 3B will be shortcircuited since these electrodes 3A and 3B are manufactured by way of the above-described thin-film fabricating means.
As a result, since, as previously described, the gap "L" between the electrodes 3A and 3B cannot be made considerably narrow, the large photoelectric current cannot be expected. Otherwise, the higher response speed cannot be realized.